Panel material and method of manufacturing the same

ABSTRACT

The panel material of the present invention comprises (A) two sheets of FRP molded board as upper and lower surface materials, and, as a core material, (B) a high density, rigid polyurethane foam layer which has been obtained by injecting a rigid polyurethane foam starting material between these two sheets of FRP molded board and allowing this starting material to foam, and which has a closed cell structure and a density of 0.2˜0.5 g/cm 3 . In addition, the manufacturing method of the panel material of the present invention includes a process for obtaining an integrally molded sandwich panel by injecting a rigid polyurethane foam starting material into a space between two sheets of FRP molded board which have been set in a mold, and allowing it to foam; and a process in which panel material is made by cutting this sandwich panel to a desired size. The panel material of the present invention is particularly suitable for use as flooring in vehicles such as trucks, buses, railway rolling stock, freight containers, and the like.

TECHNICAL FIELD

The present invention relates to a panel material and a manufacturingmethod therefor. This panel material is superior in its light weightproperties, rigidity, and impact resistance. Furthermore, it is superiorin properties for processing by a cutting and properties for fixation bya screw, and it can be easily cut to a desired size. In more detail, thepresent invention relates to a panel material for use as a flooringmaterial for vehicles such as trucks, buses, railway rolling stock,freight containers and the like; and to a manufacturing method for thispanel material.

BACKGROUND OF THE INVENTION

Conventionally, as is known, timber has been widely used as the materialfor vehicle parts such as flooring, walls and roofing. However, inrecent years, regulation of the felling of tropical and subtropicalforests has been strengthened from the perspective of environmentalprotection, and the use of timber even for vehicle parts is alsobecoming difficult. In addition, with regard to transportation vehiclessuch as trucks, buses, railway rolling stock, freight containers and thelike, in response to recent improvements in transportation and to thestrengthening of legal regulations, increases in load capacity aredemanded, and, in particular, with regard to trucks, in the 1994revision of the Road Traffic Act in Japan, controls on overloading werestrengthened, and increases in load capacity by means of weightreduction of vehicle materials are pressing.

As a result, in recent years, an aluminum honeycomb panel and the likehave become used in large quantities in vehicle materials with the goalof weight reduction and increased rigidity. However, an aluminumhoneycomb panel not only increase costs, but it is difficult to cut tothe desired size, and there is the processing problem that, as it is, itcannot be held to the frame using screws, therefore, it is not cominginto wide use as material which replaces timber.

In addition, when used as a flooring material for vehicles, an aluminumhoneycomb panel is weak with regard to concentrated loads; when a loadis concentrated on a small area, that area becomes dented, andtherefore, it is unable to withstand practical use.

For this reason, the use of resin foams, which are sometimes calledsynthetic woods as flooring for vehicles has also been proposed. Theseare reinforced and their rigidity increased by glass fibers within theresin foam, however, this is not sufficient, and to cover the lack inrigidity, they are generally made thicker. For this reason, even thoughthe specific weight of the resin foam itself is low, by weight per unitof area, the weight reduction is not always sufficient. In addition, thehardness of the surface of resin foams is low and this is unfavorablefrom the point of view of durability. There is also a problem withproperties for fixation by screws such that screws are not veryeffective at holding the resin foams to a frame during installation.

An objective of the present invention is the development of a flooringmaterial for vehicles which eliminates these problems, is superior inits light weight properties, rigidity, and impact resistance, and issuperior in its cutting processability such that it can be freely cutinto members of desired size and in its properties for fixation by screwsuch that it can be held in place by screws.

DISCLOSURE OF THE INVENTION

As a result of conducting research on various aspect of the abovementioned problems, the inventors of the present invention have reachedthe perfection of the present invention by means of a special foam whichdoes not contain reinforcing fiber materials and surface materialmanufactured from fiber reinforced plastic (FRP).

In more detail, the present invention provides a panel materialcomprising (A) two sheets of molded FRP board as the upper and lowersurface material and, (B) a high density, rigid polyurethane foam, whichis a closed cell foam and has a density of 0.2-0.5 g/cm³, which formsthe core material between the upper and lower surface members byinjection and foaming. In addition, the present invention also providesa manufacturing method for panel material comprising the process ofmolding an integrated body wherein a rigid polyurethane foam startingmaterial is injected into and allowed to foam in the space between twosheets of FRP molded board which have been placed in a mold, and aprocess of cutting the thus obtained sandwich panel into the desiredsize, wherein the specific gravity of the panel material is preferably0.3 to less than 0.6. It is possible to carry out processes such ascutting and making holes easily on the panel material on site; the FRPmolded sheet (A) preferably uses at least one layer of cloth reinforcingfiber material as the reinforcing fiber material, and uses a heatcurable resin as the matrix resin; since the high density, rigidpolyurethane foam (B) does not contain reinforcing fiber material, it ispreferable that the flexural modulus be 14-200 kgf/mm², and that thereduction in thickness be 10% or greater after the foam has beencompressed to 50% deformation and then the compression pressurereleased. It is preferable that the heat curable resin of the FRP moldedboards (A) be a radical polymerizable unsaturated resin, and that theweight of the reinforcing fiber material is 100-800 g/m² per sheet offiber material and a plurality of sheets of fiber material are used suchthat the total amount of fiber per FRP molded board is 800-1700 g/m² ;the thickness of the FRP molded board (A) is 0.6 to less than 3.0 mm perboard, and the thickness of the rigid urethane foam (B) is 5-24 mm. Thepanel material is preferable for flooring for vehicles; and the vehiclesare vehicles for transportation such as trucks, buses, railway rollingstock, freight containers and the like.

BEST MODE FOR CARRYING OUT THE INVENTION

The FRP molded board used in the present invention is preferably a boardformed by impregnating the reinforcing fiber material with a heatcurable resin, and allowing it to harden. As the heat curable resin, forexample, unsaturated polyester resin, phenol resin, epoxy resin, andvinylester resin can be mentioned, and, more preferable are radicalpolymerizable unsaturated resins (for example, unsaturated polyesterresin), and vinyl ester resins (for example, epoxy acrylate resin,urethane acrylate resin, and unsaturated polyester acrylate resin). ThisFRP molded board is a molded board which has superior characteristicsfrom the point of view of mechanical properties, such as surfacehardness, flexural modulus and the like, and from the point of view ofease of carrying out operations such as cutting on site; and whichpreferably uses an unsaturated polyester type resin and, additionally, aresin of the type which hardens after being impregnated is preferablefrom the point of view of physical properties.

As the reinforcing fiber material used in the FRP molded board,preferably glass fibers are used, but, of course, in order to furtherlighten weight, carbon fibers, organic type high modulus fibers such asaramid fiber, non-woven fabric and the like can be used, or the use ofthese together with glass fibers is also possible.

With regard to the form of the reinforcing fiber material which is usedin the FRP molded board, for example, chopped strand mat, roving, rovingcloth, cloth, and the like can be mentioned, and any of these can beused, but when the present invention is being used as vehicle flooring,in order to withstand localized loads, the provision of at least onelayer of cloth (mesh) reinforcing fiber material is preferable. As thecloth reinforcing fiber material, glass cloth and roving cloth arepreferably mentioned.

With regard to the reinforcing fiber material of the present invention,it is preferable to use a plurality of sheets of reinforcing fibermaterial such that the total fiber content used is 800-1700 g/m² per FRPmolded board, and such that the fiber content per sheet of fibermaterial is 100-800 g/m². It is preferable that a combination of matform and cloth form be used. The mat form is preferably one sheet ofchopped strand mat having a fiber content of 150-600 g/m², and the clothform is preferably one sheet of roving cloth having a fiber content of100-800 g/m².

The proportion of reinforcing fiber material used in the FRP moldedboard is preferably between 20-70% by weight, and more preferably30-50%. These values are also suitable when carbon fibers, organic typehigh modulus fibers such as aramid fibers, non-woven fabric are used, orwhen they are used in combination. When the proportion of reinforcingfiber material is less than 20%, it is not possible to obtain asatisfactory flexural modulus, and when it is greater than 70% impactresistance is degraded, therefore, these conditions are not desirable.

The thickness of the FRP molded board is preferably 0.6 mm or greaterand less than 3.0 mm. When it is less than this, there are problems withimpact resistance and flexural properties, and when it is thicker thanthis, use as flooring for vehicles is difficult from the point of viewof weight, cost and the like.

The manufacturing method for the FRP molded board is not particularlylimited, and those manufactured by means of known methods can be usedwithout problem. As an example of an outline of this manufacturingmethod, firstly, a glass mat or the like is impregnated with a heatcurable resin such as unsaturated polyester resin, then, this is curedfor one hour in a drying oven at 60° C., and then removed from the moldand cut to the desired dimensions to give a board which can be used.

It is preferable for the FRP molded board and the rigid polyurethanefoam to adhere directly, and for FRP molded boards which have pooradhesive properties, it is preferable to apply a primer or to sand thecontact surface for the core material in advance. This is for thepurpose of improving the adhesive properties of the FRP molded boardwhich is the surface material and the rigid urethane foam during theprocess in which the rigid polyurethane foam starting material isinjected and foams.

As the core material, there is rigid polyurethane foam, but to achievethe necessary objectives of the present invention, superior processingproperties, mechanical strength, particularly, flexural strength, andflexural modulus are required and, therefore, the rigid polyurethanefoam is a closed cell type.

Since the rigid polyurethane foam does not contain reinforcing fibermaterial, it is preferable for the flexural modulus to be 14-200Kgf/mm², and for the reduction in thickness to be 10% or greater afterthe foam has been compressed to 50% deformation and then the compressionpressure released.

The rigid polyurethane foam starting material used in the presentinvention refers to starting material for manufacturing rigidpolyurethane foam or rigid urethane modified polyisocyanurate foam.These are preferably obtained from polyol compounds and polyisocyanates.

Here, the polyol compound which is used in the present invention refers,in the main, to compositions comprising polyol, catalyst, bubble sizecontrolling agents, foaming agents, flame retardants, and the like.

From among these, firstly, as the above-mentioned polyol, for example,substances having a structure in which an alkylene oxide is added to acompound having at least two activated hydrogen atoms, or the like, orvarious polvetherpolyols which are mixtures of these substances;polyesterpolyols prepared from polyhydric alcohol and polycarboxylicacid or lactone compounds; and, additionally, polyetheresterpolyolshaving both ether linkages and ester linkages can be mentioned.

As the polyetherpolyol, giving only particular representative examples,there are compounds in a form obtained by adding initiators to any typeof alkylene oxides, such as ethylene oxide, propylene oxide and butyleneoxide, wherein polyhydric alcohols, polyhydric phenols, and amines canbe used respectively as the initiator.

In addition, as the initiators used in these polyetherpolyols, givingonly particular representative examples, firstly, as the polyhydricalcohol, there are, to start with, various dihydric alcohols such asethylene glycol, propylene glycol, butanediol, hexanediol, diethyleneglycol, neopentyl glycol, or 3-methyl-1,5-pentanediol; in addition,there are various trihydric alcohols such as glycerin,trimethylolpropane, hexanetriol, or trimethylolethane; and varioustetravalent or greater alcohols such as pentaerythritol, sorbitol,methylglucoside, or cane sugar. As the polyhydric phenol, there arecompounds such as pyrogallol or hydroquinone; or there are, in additionto these, various compounds such as various bisphenols such as bishpenolA.

In addition, as the polycarboxylic acid, giving only particularrepresentative examples, there are various aliphatic polycarboxylicacids such as succinic acid, oxalic acid, or adipic acid; and variousaromatic polycarboxylic acids such as phthalic acid, trimellitic acid,or HET acid.

In addition, as the amine, giving only particular representativeexamples, there are various monoamines such as ammonium, alkylamine oraniline; various polyamines such as ethylenediamine, diethylenetriamine,tolylenediamine, piperazine, diaminodiphenylmethane, oraminoethylpiperazine; and various alkanolamines such asmonoethanolamine, diethanolamine, triethanolamine, monopropanolamine,dipropanolamine or tripropanolamine.

As the polyesterpolyol, giving only particular representative examples,as the glycol component, various dihydric alcohols such as ethyleneglycol, propylene glycol, butanediol, hexanediol, diethylene glycol,dipropylene glycol, neopentyl glycol, or 3-methyl-1,5-pentanediol;various trihydric alcohols such as glycerin, trimethylolpropane ortrimethylolethane; or various tetravalent or greater polyhydric alcoholssuch as pentaerythritol, or the like can be used. In addition, as thecarboxylic acid component, those which have a form which can be obtainedby using various aliphatic polycarboxylic acids such as succinic acid,oxalic acid, or adipic acid; or various aromatic polycarboxylic acidssuch as phthalic acid, trimellitic acid, or HET acid can be mentioned.

In the manufacture of the polyetheresterpolyol, for example, a polyolcan be used which has a combination within the molecule of etherlinkages and ester linkages, and which is obtained by using theabove-mentioned various starting materials.

From among these, polyetherpolyols having a form obtained usingaliphatic compounds as initiators are preferable, and polyetherpolyolshaving a form obtained using polyhydric alcohols or amines as initiatorsare more preferable, and various polyetherpolyols such as thosementioned above which have a hydroxyl value of 700 (mg KOH/g) or lessare even more preferable.

Polyol compounds in a form which uses 20% by weight or greater of thispolyetherpolyol are superior in compatibility with fluorine halogenatedhydrocarbon foaming agents, and are, therefore, particularly preferable.

As the foaming agents, water which is a kind of reactive foaming agentand fluorine containing hydrocarbons or fluorine halogenatedhydrocarbons which have, in accordance with need, at least one hydrogenatom within the molecule can also be used. As the relevant fluorinecontaining (halogenated) hydrocarbon, giving only representativeexamples, trifluoromethane, difluoromethane, pentafluoroethane,difluoroethane, dichloromonofluoromethane, monochloromonofluoromethane,monochlorodifluoromethane, dichlorotrifluoroethane,dichlorofluoroethane, monochlorotetrafluoroethane,monochlorodifluoromethane, monochlorodifluoroethane, and the like can beused.

In addition, it is also possible to use halogenated hydrocarbons, suchas methylenechloride, which have low boiling points in combination withthe above.

As the above-mentioned polyisocyanate which is used in the presentinvention, giving only particular representative examples, variousaliphatic type polyisocyanates such as hexamethylene diisocyanate;various alicyclic isocyanates such as hydrogenated diphenylmethanediisocyanate or isophorone diisocyanate; various aromatic isocyanatessuch as tolylene diisocyanate (TDI) and diphenylmethane diisocyanate(MDI); in addition, crude TDI; crude MDI; isocyanate modifiedprepolymers; or isocyanurate modified prepolymers; and the like can bementioned.

In addition, as the above-mentioned catalyst used in the presentinvention, giving only particular representative examples, various aminetype catalysts such as hexamethylenediamine, pentamethyldiethyltriamine,or imdazol; catalysts for manufacturing various urethane modifiedpolyisocyanurates/foams such as potassium octylate and triazine; andmetal containing catalysts such as dibutyltindilaurate (DBTL) and thelike can be mentioned.

The rigid polyurethane foam (B) used in the present invention has adensity of 0.2-0.5 g/cm³. When the density is lower than this, thestrength of the foam is reduced, therefore, the flexural modulus,flexural strength, etc., of the panel material (and, in particular, ofthe flooring material for vehicles) of the present invention arereduced, and, in addition, buckling occurs in the foam layer underconcentrated loads. On the other hand, when the density of the foamlayer is greater than 0.5 g/cm³, the weight of the panel material of thepresent invention increases, particularly when it is used for flooringfor vehicles, and this is also not desirable from the point of view ofcost. A density of 0.25-0.35 g/cm³ is even more preferable.

In addition, a closed cell structure is preferable mainly from the pointof view of mechanical strength. The closed cell ratio is preferably 80%or greater and even more preferably 90% or greater. In addition, thecell size of the rigid polyurethane foam is not particularly limited,but a cell diameter of 1-1000 microns is good from the point of view ofstrength, molding properties, and the like.

The thickness of the high density, rigid polyurethane foam of the corematerial used in the present invention is determined by considering thethickness of the finally obtained panel and the thickness of the FRPmolded board, and is preferably 5-24 mm.

The thickness of the panel material of the present invention ispreferably 10˜30 mm. When the thickness of the panel material is greaterthan this, not only is the weight increased, but it is disadvantageousfrom the point of view of capacity, and cost increase, therefore, thiscondition is not desirable. If the thickness of the panel material ismade thinner than this, there are problems from the point of view ofstrength and from the point of view of bending. The specific gravityofthe panel is preferably 0.3 to less than 0.6. If the specific gravityis greater than this the light weight property is degraded.

In the manufacturing method of the panel material of the presentinvention, two sheets of FRP molded board are set, using spacers, at thedesired spacing which corresponds to the desired thickness for the panelmaterial in a box mold maintained at a temperature of preferably 30-70°C. Next, the above-mentioned rigid polyurethane foam starting materialis injected into the space therebetween and is allowed to foam to apredetermined expansion ratio, preferably 2-10 times, within the mold.Afier the foam of the above-mentioned polyurethane foam startingmaterial has hardened, a sandwich panel material is removed from theabove-mentioned box shaped mold and this sandwich panel material has anFRP molded board/rigid polyurethane foam layer/FRP molded boardstructure and is the starting material for the flooring for vehicles.

Next, the panel material is made by cutting this sandwich panel materialto the desired size, in accordance with need. For example, for asituation in which the panel material is used for the flooring of atruck, the width is preferably 900-1500 mm, and the length is 2000-2400mm.

For panel material obtained in this way, the proportion of the weightsof the FRP molded board (A) and the rigid polyurethane foam (B) ispreferably (A)/(B)=15-75/85-25 (% by weight), and more preferably25-65/35-75 (% by weight).

In addition, in accordance with need, and mainly from the point of viewof appearance and durability, a synthetic resin, such as unsaturatedpolyester type resin, acrylic type resin, urethane type resin, melaminetype resin or the like, which has been colored so as to be the samecolor as the above-mentioned FRP molded board which is the surfacematerial, can also be applied to the surface of the cut edge (the cutsurface, and the surface of the cut end of the foam) of the cut panel.In addition, a protective material can also be arranged on all foursides and corners.

The form of the surface of the panel material of the present inventioncan be curved, flat, or irregular, but a flat surface panel ispreferable. This surface may be sanded, and is preferably a surfacehaving small irregularities with a pattern or without a pattern. Thesesanded surfaces, and irregularities can also serve to prevent slipping.

The form of the pattern of the irregularities in the surface is notparticularly limited, but preferably it has indentations of a embossedpattern, straight line pattern, curved line pattern, or lattice pattern,and the width of the grooves is of the level of 0.1-20 mm. In addition,a small form of the above-mentioned irregular pattern may be includedwithin a large circle or square pattern.

As the vehicles for the vehicle flooring material, for example,transportation vehicles such as trucks, buses, railway rolling stock,freight containers, ships, and airplanes can be mentioned, and theplatform flooring of freight containers and trucks can be preferablymentioned.

Since the panel material obtained by means of the present invention canbe used in the same way as general wood materials, for example, it canbe cut using saws, nailed, held by screws and holes can be made in it,it is superior in processability, and the machines, tools, etc., whichhave been used in the past can be used as they are.

EMBODIMENTS

In the following, the present invention is explained based on theembodiments, and except where otherwise stated, "parts" and "%" arebased on weight.

Embodiment 1

Two sheets of chopped strand mat of 450 g/m² as the reinforcing fibermaterial were overlapped, and impregnated with unsaturated polyesterresin, then this unsaturated polyester resin was allowed to cure, and,thereby, FRP molded board A for use in the surface material wasobtained. The thickness of this FRP molded board A was 1.5 mm and theproportion of reinforcing fiber material was approximately 40% byweight.

Next, two sheets of FRP molded board A were set into a box shaped moldof 1 m×2.5 m×15 mm maintained at 45° C., rigid polyurethane foamstarting material was injected into the space between these FRP moldedboards A and allowed to foam, and, thereby, a sandwich panel moldedproduct (having a thickness of 15 mm and a specific gravity of about0.5) was obtained for which the thickness of the rigid polyurethane foamlayer was 12 mm and the density of the rigid polyurethane foam layer was0.3 g/cm³.

The rigid polyurethane foam starting material used in this case was acombination of crude 4,4'-diphenylmethanediisocyanate (MDI) and a polyolcompound comprising 100 parts of a polyhydric alcohol typepolyetherpolyol having a hydroxyl value of 450 and prepared usingpentaerythritol as an initiator, 1.0 parts of water as a foaming agent,and 0.5 parts of hexamethylenediamine as a catalyst.

The flexural modulus of this rigid urethane foam was 35 kgf/mm², and thereduction in thickness was 20% after the foam had been compressed to 50%deformation and then the compression pressure released.

Next, this sandwich panel was cut to a size of 900×2400 mm and evaluatedas flooring for a vehicle. The results are shown in Table 1.

Embodiment 2

Roving cloth having 300 g/m² and in a mesh form, chopped strand mathaving 300 g/m², and roving cloth having 300 g/m² and in a mesh formwere overlapped in that order as the reinforcing fiber material, theywere then impregnated with unsaturated polyester resin, and allowed toharden, and, thereby, FRP molded board B for use as surface material wasobtained. The thickness of this FRP molded board B was 1.5 mm and theproportion of reinforcing fiber material was approximately 40% byweight.

Next, two sheets of FRP molded board B were set into a box shaped moldof 1 m×2.5 m×15 mm maintained at 45° C. Rigid polyurethane foam startingmaterial was injected into the space between these FRP molded boards Band allowed to foam, and, thereby, a sandwich panel molded product(having a thickness of 15 mm and a specific gravity of about 0.5) wasobtained for which the thickness of the rigid polyurethane foam layerwas 12 mm and the density of the rigid polyurethane foam layer was 0.3g/cm³.

The rigid polyurethane foam starting material used in this case was thesame as that used in Embodiment 1. The results are shown in Table 1. Theflexural modulus of this rigid urethane foam was 35 kgf/mm², and thereduction in thickness was 20% after the foam had been compressed to 50%deformation and then the compression pressure released.

Next, this sandwich panel was cut to a size of 900×2400 mm and evaluatedas flooring for a vehicle. The results are shown in Table 1.

Embodiment 3

Chopped strand mat having 230 g/m², roving cloth having 440 g/m², andchopped strand mat having 230 g/m² were overlapped in that order as thereinforcing fiber material, they were then impregnated with unsaturatedpolyester resin, and the unsaturated polyester resin allowed to harden,and, thereby, FRP molded board C for use as surface material wasobtained. The thickness of this FRP molded board C was 1.5 mm and theproportion of reinforcing fiber material was approximately 40% byweight.

Next, two sheets of FRP molded board C were set into a box shaped moldof 1 m×2.5 m×15 mm maintained at 45° C. Rigid polyurethane foam startingmaterial was injected into the space between these FRP molded boards Cand allowed to foam, and, thereby, a sandwich panel molded product(having a thickness of 15 mm and a specific gravity of about 0.5) wasobtained for which the thickness of the rigid polyurethane foam layerwas 12 mm and the density of the rigid polyurethane foam layer was 0.3g/cm³.

The rigid polyurethane foam starting material used in this case was acombination of crude 4,4'-diphenylmethanediisocyanate (MDI) and a polyolcompound comprising 100 parts of a polyhydric alcohol typepolyetherpolyol having a hydroxyl value of 450 and prepared by usingpentaerythritol as an initiator, 10 parts of monofluoroethane and 0.5parts of water as foaming agents, and 0.5 parts of hexamethylenediamineas a catalyst.

The flexural modulus of this rigid urethane foam was 35 kgf/mm², and thereduction in thickness was 20% after the foam had been compressed to 50%deformation and then the compression pressure released.

Next, this sandwich panel was cut to a size of 900×2400 mm and evaluatedas flooring for a vehicle. The results are shown in Table 2.

Embodiment 4

Roving cloth having 300 g/m² and in a mesh form, two sheets of choppedstrand mat having 450 g/m², and roving cloth having 300 g/m² and in amesh form were overlapped in that order as the reinforcing fibermaterial, they were then immersed in unsaturated polyester resin, andallowed to harden, and, thereby, FRP molded board D for use as surfacematerial was obtained. The thickness of this FRP molded board D was 2.5mm and the proportion of reinforcing fiber material was approximately40% by weight.

Next, two sheets of FRP molded board D were set into a box shaped moldof 1 m×2.5 m×20 mm maintained at 45° C. Rigid polyurethane foam startingmaterial was injected into the space between these FRP molded boards Dand allowed to foam, and, thereby, a sandwich panel molded product(having a thickness of 20 mm and a specific gravity of about 0.55) wasobtained for which the thickness of the rigid polyurethane foam layerwas 15 mm and the density of the rigid polyurethane foam layer was 0.22g/cm³.

The rigid polyurethane foam starting material used in this case was thesame as that used in Embodiment 1. The results are shown in Table 2. Theflexural modulus of this rigid urethane foam was 16 kgf/mm², and thereduction in thickness was 25% after the foam had been compressed to 50%deformation and then the compression pressure released.

Next, this sandwich panel was cut to a size of 900×2400 mm and evaluatedas flooring for a vehicle. The results are shown in Table 2.

Embodiment 5

Chopped strand mat having 450 g/m², roving cloth having 800 g/m², andchopped strand mat having 450 g/m² were overlapped in that order as thereinforcing fiber material, they were then immersed in unsaturatedpolyester resin, the unsaturated polyester resin allowed to harden, and,thereby, FRP molded board E for use as surface material was obtained.The thickness of this FRP molded board E was 2.8 mm and the proportionof reinforcing fiber material was approximately 45% by weight.

Next, two sheets of FRP molded board E were set into a box shaped moldof 1 m×2.5 m×30 mm maintained at 45° C. Rigid polyurethane foam startingmaterial was injected into the space between these FRP molded boards Eand allowed to foam, and, thereby, a sandwich panel molded product(having a thickness of 29.6 mm and a specific gravity of about 0.50) wasobtained for which the thickness of the rigid polyurethane foam layerwas 24 mm and the density of the rigid polyurethane foam layer was 0.25g/cm³.

The rigid polyurethane foam starting material used in this case was thesame as that used in Embodiment 1. The results are shown in Table 2. Theflexural modulus of this rigid urethane foam was 23 kgf/mm², and thereduction in thickness was 23% after the foam had been compressed to 50%deformation and then the compression pressure released.

Next, this sandwich panel was cut to a size of 900×2400 mm and evaluatedas flooring for a vehicle. The results are shown in Table 2.

Comparative Example 1

This was conducted in the same way as Embodiment 1 with the exceptionthat commercially available plywood having a thickness of 15 mm was usedas the surface material for Comparative Example 1. In addition, thespecific gravity of this plywood was 0.7. The results are shown in Table1.

Comparative Example 2

This was conducted in the same way as Embodiment 1 with the exceptionthat commercially available aluminum honeycomb panel having a thicknessof 15 mm was used as the surface material for Comparative Example 2. Inaddition, the thickness of the aluminum sheets of the surfaces of thisaluminum honeycomb panel were each 1.0 mm, and the specific gravity ofthis aluminum honeycomb panel was 0.7. The results are shown in Table 1.

Comparative Example 3

Two sheets of FRP molded board A, the same as those used in Embodiment1, were set into a box shaped mold of 1 m×2.5 m×20 mm maintained at 45°C. Next, rigid polyurethane foam starting material was injected into thespace between these FRP molded boards A and allowed to foam, and,thereby, a sandwich panel molded product (having a thickness of 15 mmand a specific gravity of about 0.4) was obtained for which thethickness of the rigid polyurethane foam layer was 12 mm and the densityof the rigid polyurethane foam layer was 0.1 g/cm³.

The rigid polyurethane foam starting material used in this case was acombination of crude 4,4'-diphenylmethanediisocyanate (MDI) and a polyolcompound comprising 100 parts of a polyhydric alcohol typepolyetherpolyol having a hydroxyl value of 450 and prepared by usingpentaerythritol as an initiator, 20 parts of monofluoroethane and 2parts of water as foaming agents, and 0.5 parts of hexamethylenediamineas a catalyst.

The flexural modulus of this rigid urethane foam was 8 kgf/mm², and thereduction in thickness was 35% after the foam had been compressed to 50%deformation and then the compression pressure released. The results areshown in Table 2.

                                      TABLE 1    __________________________________________________________________________                            Comparative                                    Comparative            Embodiment 1                    Embodiment 2                            Example 1                                    Example 2    __________________________________________________________________________    specific gravity            0.5     0.5     0.7     --    of product    weight of            7.5     7.5     10.5    8.8    product (Kg/m.sup.2)    thickness of            15      15      15      15    product (mm)    surface hardness            90      90      50      98    (Shore-A)    flexural strength            500     600     500     500    (Kg/cm.sup.2)    compression            1500    1800    950     450    breaking strength    (Kg)    repetition            900 Kg, 900 Kg, 900 Kg, 900 Kg,    compression test            broke at 4000                    no abnormalities                            broke at 300                                    broke at first            times   at 10,000 times                            times   time    abrasion            0.09    0.09    0.35    --    resistance (cm.sup.3)    cutting can be cut using                    can be cut using                            can be cut using                                    requires special    processability            normal wood                    normal wood                            normal wood                                    devices for metal            panel saw                    panel saw                            panel saw                                    processing    ability to be held            can be held                    can be held                            can be held                                    requires insertion    by screw            directly to the                    directly to the                            directly to the                                    of wood or the            frame by screws                    frame by screws                            frame by screws                                    like in the screw                                    holding section    need for coating            not necessary                    not necessary                            necessary                                    not necessary    __________________________________________________________________________     Note:     Surface hardness: measured using a ShoreD hardness meter     Compression Breaking and Repetition Compression Tests: the diameter of th     indentor was 20 mm; the compression rate was 100 mm/minute     Abrasion Resistance: Taper abrasion test (abrasion wheel H22, load 1 Kg,     1000 times)     Requirement for Coating: For Comparative Example 1, for the panel as it     was, due to problems such as very powerful absorption of water, faster     deterioration, and weight increase due to absorption of water, in general     a coating was necessary.

                                      TABLE 2    __________________________________________________________________________                                    Comparative            Embodiment 3                    Embodiment 4                            Embodiment 5                                    Example 3    __________________________________________________________________________    specific gravity            0.5     0.55    0.5     0.4    of product    weight of            7.5     11.0    15.0    6.0    product (Kg/m.sup.2)    thickness of            15      20      29.6    15    product (mm)    surface hardness            90      90      90      90    (Shore-A)    flexural strength            700     900     1000    350    (Kg/cm.sup.2)    compression            1900    2100    2500    700    breaking strength    (Kg)    repetition            900 Kg, 900 Kg, 900 Kg, 900 Kg,    compression test            no abnormalities                    no abnormalities                            no abnormalities                                    broke at first            at 10,000 times                    at 10,000 times                            at 10,000 times                                    time    abrasion            0.09    0.09    0.09    0.09    resistance (cm.sup.3)    cutting can be cut using                    same as in                            same as in                                    can be cut using    processability            normal wood                    column to left                            column to left                                    normal wood            panel saw               panel saw    ability to be held            can be held                    same as in                            same as in                                    requires insertion    by screw            directly to the                    column to left                            column to left                                    of wood or the            frame by screws         like in the screw                                    holding section    need for coating            not necessary                    not necessary                            not necessary                                    not necessary    __________________________________________________________________________     Note:     The measurement conditions for Surface hardness, Compression Breaking and     Repetition Compression Tests, and the measurement method for Abrasion     Resistance were the same as shown in the "Note" for Table 1.

From the above, it can be understood that the panel material of thepresent invention has high rigidity at a light weight, is superior inproperties for processing and can easily be cut to a desired size.

Industrial Applicability

The present invention provides a panel material which is superior insurface hardness and abrasion resistance due to the use of FRP moldedboards as surface material; furthermore, by means of injecting a rigidpolyurethane foam starting material into the space between two sheets ofFRP molded board, allowing it to foam and, thereby, forming a sandwichpanel having a specific density, the panel material is superior inrigidity and in being light weight and the adhesive force at the borderbetween FRP molded board and the foam is strong; and, in addition, thepanel material is superior in processing properties such that it can befreely cut to a desired size, and in its ability to be fixed by screwssuch that it can be held in place by screws. Consequently, the panelmaterial of the present invention is particularly suitable for use asvehicle flooring for trucks, buses, railway rolling stock, freightcontainers, and the like. In addition, the panel material of the presentinvention can also be used in a large number of other fields as areplacement for wood panels, for example, for notice boards; panels foruse in sports facilities; table tops; all types of flooring; wallmaterials; and the like.

We claim:
 1. A panel material comprising(A) two sheets of fiberreinforced plastic (FRP) molded board as upper and lower surfacematerials; and (B) a high density, rigid polyurethane foam as a corematerial having a density of 0.2-0.5 g/cm³ and a closed cell structure,said high density, rigid polyurethane foam having been obtained byfoaming between said two sheets of fiber reinforced plastic moldedboard, wherein a thermal curable resin of said fiber reinforced plasticmolded board (A) is a radical polymerizable unsaturated resin, andsheets of reinforcing fiber material having a fiber weight of 100-800g/m² per sheet are used, and a total amount of said reinforcing fibermaterial per said fiber reinforced plastic molded board is 800-1700g/m².
 2. A panel material according to claim 1, wherein a specificgravity of said panel material is 0.3 to less than 0.6, and processes ofcutting and hole making can be performed on said panel material on site.3. A panel material according to claim 1, wherein said fiber reinforcedplastic molded board (A) includes at least one layer of cloth-formreinforcing fiber material.
 4. A panel material according to claim 1,wherein a flexural modulus of said high density, rigid polyurethane foam(B) is 14-200 kgf/mm², and a reduction in thickness is 10% or greaterafter said foam has been compressed to 50% deformation and compressionpressure released.
 5. A panel material according to claim 1, wherein athickness of said fiber reinforced plastic molded board (A) is 0.6 toless than 3.0 mm per board and a thickness of said rigid urethane foam(B) is 5-24 mm.
 6. A panel material as recited in any of claims 1 to 5wherein said panel material is flooring for a vehicle.
 7. A method ofmanufacturing the panel material of claim 1 comprising:a process formolding an integrated body wherein a rigid polyurethane foam startingmaterial is injected into a space between two sheets of fiber reinforcedplastic molded board set in a mold, and allowed to foam; and a processin which a thus obtained sandwich panel is cut into a desired size.